Effects of Mn addition on microstructure and mechanical properties of (Al+x at.%Mn)3Ti intermetallic compounds prepared by mechanical alloying and spark plasma sintering

Effects of Mn addition on microstructure, phase stability and mechanical properties of (Al+x at.%Mn)3Ti intermetallic compounds fabricated by mechanical alloying and spark plasma sintering were investigated. As-milled ternary powders consist of homogeneous distribution of fine crystallites in amorphous matrix. (Al+0.08 Mn)3Ti showed the most stable thermal stability with average grain sizes of less than 60 and 100 nm after heat treatments at 900 and 1100 °C, respectively. The reduction of grain size down to nano-scale was not sufficient enough to increase the fracture toughness of trialuminide. Fracture toughness was also remained relatively constant and showed no significant dependence on Mn concentration. Microhardness was generally increased with increasing Mn concentration and decreased with increasing heat treatment temperatures due to the grain size effects. The formation of L12 phase played a major role in increased fracture toughness and (Al+0.08 Mn)3Ti showed the highest fracture toughness of 4.12 MPa m1/2 with only L12 phase formation.